Methods and apparatus for shallow gradient artifact reduction in image display systems

Patent metadata

Field	Value
Publication number	US-2018199014-A1
Application number	US-201815913556-A
Country	US
Kind code	A1
Filing date	Mar 6, 2018
Priority date	Nov 14, 2016
Publication date	Jul 12, 2018
Grant date	—

Abstract

In described examples, a method includes: receiving an array of image data pixels for display by a spatial light modulator; dividing the array of image data pixels into a plurality of blocks. For the blocks of the plurality of blocks, the method includes: computing a mean value for pixels in the block; computing a variance for pixels in the block; and, in response to the mean value and the variance, retrieving an indicator of a likelihood of a visible artifact for the block; and in response to the retrieved indicator, outputting a signal to selectively increase or reduce a load time of the spatial light modulator for displaying the array of image data pixels.

First claim

What is claimed is:

1 . A method, comprising:
receiving an array of image data pixels for display by a spatial light modulator, wherein each pixel has respective first, second and third color components; dividing the array of image data pixels into a plurality of blocks; per block of the plurality of blocks: computing a first mean value of the first color component for the pixels in the block; computing a second mean value of the second color component for the pixels in the block; computing a third mean value of the third color component for the pixels in the block; computing a first variance of the first color component for the pixels in the block; computing a second variance of the second color component for the pixels in the block; computing a third variance of the third color component for the pixels in the block; and, in response to the first, second and third mean values and the first, second and third variances, retrieving at least one respective indicator of a likelihood of a visible artifact for the block; computing an aggregate indicator in response to the retrieved respective indicators for all of the blocks; and in response to the computed aggregate indicator, outputting a signal to adjust a time between successive loadings of the spatial light modulator for displaying the array of image data pixels, wherein the likelihood of the visible artifact is reduced by reducing the time between the successive loadings, and the likelihood of the visible artifact is increased by increasing the time between the successive loadings.

2 . The method of claim 1 , wherein the visible artifact is a visible pulse width modulation temporal contour artifact.

3 . The method of claim 1 , wherein the array is a two-dimensional array.

4 . The method of claim 1 , wherein retrieving the respective indicators comprises: using the mean values and the variances as address values to retrieve the respective indicators from a memory.

5 . The method of claim 1 , wherein outputting the signal comprises:
per block, in response to the retrieved at least one respective indicator, selectively clearing or setting at least one respective binary flag for the block, wherein the at least one respective binary flag is stored in a memory; summing the respective binary flags to form a summation value; comparing the summation value to a threshold value; and responsive to the comparing, outputting the signal.

6 . The method of claim 1 , further comprising:
displaying the array of image data pixels via the spatial light modulator.

7 . The method of claim 1 , wherein computing the first mean value of the first color component comprises:
per pixel in the block, adding an intensity value of the first color component of the pixel to a running sum of pixel intensity values.

8 . The method of claim 7 , wherein computing the first mean value of the first color component comprises:
computing the first mean value of the first color component by dividing the running sum of pixel intensity values by at least a number of pixels in the block.

9 . The method of claim 1 , wherein computing the first variance of the first color component comprises:
per pixel in the block, computing a squared intensity value of the first color component of the pixel, and adding the squared intensity value to a running sum of squared intensity values.

10 . The method of claim 9 , wherein computing the first variance of the first color component comprises:
computing a standard deviation for the block, in response to the first mean value and the running sum of squared intensity values.

11 . The method of claim 10 , wherein computing the standard deviation comprises:
computing the standard deviation as a square root of: the running sum of squared intensity values minus the first mean value squared.

12 . The method of claim 1 , wherein computing the first variance of the first color component comprises:
computing a difference between a maximum pixel intensity value of the first color component in the block and a minimum pixel intensity value of the first color component in the block.

13 . The method of claim 1 , wherein the method is performed separately for each of the first, second and third color components in the array of image data pixels.

14 . The method of claim 1 , wherein the spatial light modulator is one of: a digital micromirror device; and a liquid-crystal-on-silicon device.

15 . A system for displaying images, the system comprising:
a spatial light modulator to display an array of image data pixels, wherein each pixel has respective first, second and third color components; and a controller circuit to adjust a time between successive loadings of the spatial light modulator for displaying the array of image data pixels, wherein a likelihood of a visible artifact is reduced by reducing the time between the successive loadings, and the likelihood of the visible artifact is increased by increasing the time between the successive loadings; wherein the controller circuit is configured to adjust the time between the successive loadings by performing steps including: dividing the array of image data pixels into a plurality of blocks; per block of the plurality of blocks: computing a first mean value of the first color component for the pixels in the block; computing a second mean value of the second color component for the pixels in the block; computing a third mean value of the third color component for the pixels in the block; computing a first variance of the first color component for the pixels in the block; computing a second variance of the second color component for the pixels in the block; computing a third variance of the third color component for the pixels in the block; and, in response to the first, second and third mean values and the first, second and third variances, retrieving at least one respective indicator of the likelihood of the visible artifact for the block; computing an aggregate indicator in response to the retrieved respective indicators for all of the blocks; and in response to the computed aggregate indicator, outputting a signal to adjust the time between the successive loadings.

16 . The system of claim 15 , wherein the visible artifact is a visible pulse width modulation temporal contour artifact.

17 . The system of claim 15 , wherein retrieving the respective indicators comprises: using the mean values and the variances as address values to retrieve the respective indicators from a memory.

18 . The system of claim 15 , wherein outputting the signal comprises:
per block, in response to the retrieved at least one respective indicator, selectively clearing or setting at least one respective binary flag for the block, wherein the at least one respective binary flag is stored in a memory; summing the respective binary flags to form a summation value; comparing the summation value to a threshold value; and responsive to the comparing, outputting the signal.

19 . The system of claim 15 , wherein computing the first mean value of the first color component comprises:
per pixel in the block, adding an intensity value of the first color component of the pixel to a running sum of pixel intensity values.

20 . The system of claim 19 , wherein computing the first mean value of the first color component comprises:
computing the first mean value of the first color component by dividing the running sum of pixel intensity values by at least a number of pixels in the block.

Assignees

• Texas Instruments Inc

Inventors

• Morgan Dan
• Kempf Jeffrey Matthew

Classifications

• H04N9/3111

  for displaying the colours sequentially, e.g. by using sequentially activated light sources (sequential projection in colour photography G03B33/08) · CPC title

• H04N9/3123 Primary

  using pulse width modulation · CPC title

• H04N9/3179

  Video signal processing therefor · CPC title

• H04N9/3164

  using multiple light sources · CPC title

• H04N9/3155

  for controlling the light source (light source control per se H05B35/00 – H05B47/00; control of an illumination source for displays in general G09G3/3406) · CPC title